This invention relates to an improved process for the preparation of n-olefins by dehydrogenation of n-paraffins. More particularly, it relates to the selective preparation of n-olefins having from 5 to 20 carbon atoms by improvements in the process wherein n-paraffins are dehydrogenated in the presence of a catalyst comprising a noble metal on a cation mordenite base.
Olefins of this type have been prepared by a number of commercial methods including (1) thermal and catalytic cracking of petroleum fractions, (2) thermal cracking of paraffin wax, (3) dehydrochlorination of monochlorinated paraffinic hydrocarbons, (4) polymerization of low molecular weight olefins by the Ziegler process, (5) hydrogenation of fatty acids to alcohols with subsequent dehydration of the alcohol to the olefin, (6) fractionation of natural oils and resins of plants, and (7) catalytic dehydrogenation of saturated hydrocarbons. The instant invention relates to improvements in the last named method.
Straight-chain olefin compounds having from 5 to 20 carbon atoms have a variety of uses. They may be used for the synthesis of other compounds such as aldehydes, alcohols, acids and mercaptans. In addition, they are also valuable in the preparation of synthetic detergents, synthetic rubber and resins and as lubricating oil additives. By catalytic dehydrogenation of n-paraffin compounds, good conversion to olefins can be attained. However, along with the dehydrogenation reaction, a significant amount of isomerization and cyclization occurs, with the result that the product olefin comprises a mixture of various olefinic products, and the selectivity for the desired straight-chain product is often less than 50%. If one wishes to obtain pure n-olefins, it is necessary to separate the various olefin products -- a difficult task in view of the closeness in boiling points among the individual olefin hydrocarbons.
It is therefore a prime object of this invention to provide a process for the selective production of n-olefins from n-paraffins where the amount of branched-chain and cyclic by-product is about 15% less. It is another object to obtain such selectivity by improvements in the process of dehydrogenation of n-paraffins in the presence of a mordenite supported noble metal catalyst. Other objects will become apparent from the following description of the invention.